6 
ORGANOGRAPHY. 
BOOK I. 
by no means to thin transparent tissue that these j>assages are 
confined; they are universally present in the sides of the 
thickest sided tissue, where they form minute cul de sacs often 
branched, and always opening into the interior of the cell. 
They may be readily found in the gritty tissue of the pear 
{Jig. 2. a), the stone of the plum Z>, and the compact albu- 
men of seeds. Fig. 2. c represents them in the albumen of 
Alstrbmeria, where they are about yjo q of an inch in diameter. 
By what power the sedimentary matter, left on the sides of 
such tissue as this, is prevented from choking up the pits 
is at present unknown. 
It is, no doubt, very common for the pits of the membrane 
of one cell to be placed exactly opposite those of the next cell, 
as is seen in the irregular half gelatinous tissue of Cereus 
grandiflorus (see Plate II. fig. 1. « a), so that it may be 
supposed that they are passages to allow of permeation from 
one cell to another; but this arrangement is by no means 
uniform (see same fig. h).* 
Elemeritary Fibre may be compared to hair of inconceiv- 
able fineness, but it is extremely variable in size. In 
Pleurothallis ruscifolia, where it is large, I find it yoVo? 
Crinum amabile, where it is middle-sized, y y jo English 
inch in diameter. It has frequently a greenish colour, but is 
more commonly transparent and colourless. It appears to 
* For the supposed chemical difference between elementary membrane 
and fibre, see Book II. Chapter 1. 
